How are tiers spaced out.

Hey was just wondering how tiers are going to be spaced out in the game. Also do tiers take into account Vendor Trash/Normal/Green/Blue/Rare/Legendary? Trying to figure how tiers appearances are spaced out or at least how they are planned to be spaced out.|||So maybe my question wasn't the clearest in the world. So if all the different rarity of armor sets are tiers then how many are actually legendary would be one thought. Would there be one Legendary set per difficulty?
Or are tier sets counted more in the way we did it in good 'ole WoW where anything below purple is just something more substandard?
After asking this I guess one more thought would be worth mentioning. That would be how many tiers are there going to be in Inferno?
If they're all the same level would they be more related to an aesthetic or build difference? Say for instance that you have 4 tiers of gear in Inferno all legendary and each one has a theme to one of the acts, and that say for act 1 tier theme set is good for a battle mage spec where act 4 would be for a glass cannon spec.